Rodents and

Experts agree that the migratory birds triggered the
infections at the four poultry farms in the Miyazaki and Okayama prefectures over the past month. However, they also that the way the disease spread indicates that other factors were involved.

Scientists suspect rats spread the recent outbreaks of avian flu at four farms in after the H5N1 virus strain was brought over by migratory birds from China. Inspectors found that nets and coverings were in place to prevent large migratory birds from coming into contact with the poultry. Dead chickens at three of the farms were found in areas farthest from the entrance of the coops, so the wild birds were not likely the direct source of the infection.

"It's possible that small rodents, such as rats, carried the virus into the chicken coops," said Toshihiro Ito, a professor of veterinary microbiology at Tottori University who chairs the team of specialists. He said the rats were likely infected by the wild birds from China.

Ducks are also believed to be likely carriers of avian flu, because most ducks are not affected by the disease. However, the avian flu virus multiplies in the intestines of ducks and is released in their droppings. An Environment Ministry study confirmed that wild ducks were within a 10-kilometer radius of the infected farms in Japan.

"While it is necessary to prevent intrusion, it is also important to strengthen the resistance of poultry by reducing stress on the birds and improving ventilation (in the coops) to diffuse and inactivate the virus," said Hiroshi Kida, a professor of veterinary microbiology at Hokkaido University.